Set Appliance State:

Gas Off
Isolate Mains Power to appliance as per TOPs P4
Turn Hot Water Tap On
DHW temperature control to maximum
CH temperature control to minimum
Attach U-gauge to gas valve inlet pressure test point
Gas On
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Measurement:

Allow boiler to light and establish while observing the U-gauge.
Once the boiler has lit does the U-gauge show a constant inlet pressure of at least 37mb for Propane or 28mb for Butane?
Note:
When U-gauge is removed pressure test point should be tightened & checked for gas tightness.